Читать книгу A Text-book of Entomology онлайн

126 страница из 232

Loss of limbs by disuse.

In a few insects one of the claws of each foot is atrophied, as in the feet of the Pediculidæ, of many Mallophaga, all of the Coccidæ, in Bittacus, Hybusa (Orthoptera), several beetles of the family Pselaphidæ, and a weevil (Brachybamus). Hoplia, etc., bear but a single claw on the hind feet, while the allied Gymnoloma has only a single claw on all the feet. Cybister has in general a single immovable claw on the hind feet, but Cybister scutellaris has, according to Sharp, on the same feet an outer small and movable claw. In the water bugs, Belostoma, etc., the fore feet end in a single claw, while in others (Corisa) both claws are wanting on the fore feet. Corisa also has no claws on the hind feet; Notonecta has two claws on the anterior four feet, but none on the hind pair. In Diplonychus, however, there are two small claws present. (Kolbe.)

Fig. 110.—Last tarsal joint of Melolontha vulgaris, drawn as if transparent to show the inner mechanism: un, claws; str, extensor plate; s, tendon of the flexor muscle; vb, elastic membrane between the extensor plate and the sliding surface u; krh, process of the ungual joint; emp, extensor spine, and th, its two tactile hairs.—After Ockler, from Kolbe.